The present study investigated, in pair-housed male rats, whether and how the conditioned fear-induced 22-kHz USVs emitted by the ‘sender’ animal affect the behavior of its partner, the ‘receiver’ animal, when both are placed together in a novel chamber. The sender rats’ conditioned fear responses evoked significant freezing an overt evidence of fear in receiver rats that had previously experienced an aversive event but not in naïve receiver rats. Permanent lesions and reversible inactivations of the medial geniculate nucleus MGN of the thalamus effectively blocked the receivers’ freeezing response to the senders- conditioned fear responses, and this occurred in absence of lesions-inactivations impeding the receiver animals- ability to freeze and emit 22-kHz USVs to the aversive event per se.

Conclusions-Significance

These results—that prior experience of fear and intact auditory system are required for receiver rats to respond to their conspecifics- conditioned fear responses—indicate that the 22-kHz USV is the main factor for social transmission of fear and that learning plays a crucial role in the development of social signaling of danger by USVs.